Many contained spaces, such as laboratories and production areas, require either positive or negative space pressure control to prevent contaminants from either entering or leaving a designated location. It is often also necessary to control the air temperature within these pressure-controlled spaces.
Typically, to monitor and control air pressure and air temperature within the same given space, two independent feedback control systems are used. Of these two systems, the pressure control system typically has a much shorter time constant than the temperature control system. For example, the time constant of pressure control loops generally range from 15 to 60 seconds. In contrast, the time constant of space temperature control loops generally range from 5 to 15 minutes, depending on the ventilation rate in the room relative to the room's size as well as the mass of the space temperature sensor.
Due to the difference in time constants, the space pressure control is capable of varying the amount of supply air introduced into the space at a much faster rate than the space temperature control can sense and compensate for this thermo upset. As a result, significant offset levels between the actual space temperature and the desired space temperature (the room temperature setpoint) can occur. Offset levels as large as 5-10 degrees fahrenheit have been observed.
To increase the accuracy of temperature control systems which control the temperature of airspace having pressure controlled by a pressure control system, temperature control systems which employ thermo energy models have been developed. For example, such a system has been developed by Krueger, Inc., and is described in System 3: Custom DDC VAV Laboratory Ventilation Equipment published in 1988.
The Krueger temperature control system utilizes a very simple thermo energy model to decrease the time constant of its temperature control loop. The Kruger temperature control system heats supply air as it flows into a room based on the room temperature, the duct temperature, and the room temperature setpoint. However, the accuracy of the Krueger system is impeded by its failure to compensate for other temperature-affecting factors, such as the rate at which the heated air is being supplied to the room and the mass and temperature of air entering the enclosure through means other than the supply air duct of the air pressure controller.
Thus, it is clearly desirable to provide a system and method for decreasing the time constant of an air temperature control system disposed to maintain the temperature of a pressure-controlled air space. It is further desirable to provide a device and method for controlling the temperature of a room which implements a more comprehensive energy flow model than is currently provided in the art. It is further desirable to provide a system which controls the air temperature of an enclosed space with greater accuracy than is achieved by systems currently implementing energy flow models.